Production of purified pyrethrum extract



United States Patent 3,133,004 PRODUCTION OF PURIFIED PYRETHRUM EXTRACT Alan August Goldberg and Harold John Smith, Nakuru, Kenya, assignors to The Pyrethrum Board of Kenya, Nakuru, Kenya Colony, 2: body corporate of Kenya No Drawing. Filed Mar. 7, 1960, Ser. No. 12,977 Claims priority, application Great Britain Mar. 6, 1959 Claims. (Cl. 20252) This invention relates to the production of purified pyrethrum extract.

Pyrethrum extract is obtained by extracting dried ground pyrethrum flowers (Chrysanthemum cinerariaefolium) with ligroin and then evaporating the ligroin therefrom to obtain a residue, which is termed an oleoresin extract and which usually contains 25-35% of its weight of active ingredients. The active ingredients are pyrethrins I and II and cinerins I and II. These differ from each other in that the two pyrethrins contain a pentadienyl chain and the two cinerins a butenyl chain attached to the 2-position of the cyclopentenone ring. The pyrethrins differ from each other in that pyrethrin I carries a terminal methyl group whilst pyrethrin II has a terminal methoxycarbonyl group and the two cinerins I and II differ from each other in the same way. These compounds can be distilled at very low pressures without decomposition, pyrethrin I and cinerin I boil at approximately 140l50 C./10 mm., whilst pyrethrin II and cinerin II boil at approximately 190-195 C./10 mm. For the purposes of this specification mixtures of pyrethrin I and cinerin I will be referred to as pyrethrin I and mixtures of pyrethrin H and cinerin II as pyrethrin II.

According to the present invention there is provided a process for the production of a purified pyrethrum-containing composition which comprises distilling a solution of a pyrethrum oleoresin extract in a fraction of normally liquid parafiinic hydrocarbons which distils between 200 and 500 C., the distillate being carried out at a pressure which is sufliciently low substantially to avoid thermal decomposition and degradation of the pyrethrins present. The mixture of normally liquid parafiin hydrocarbons consists essentially of parafiin and cycloparafiin hydrocarbons and acts as a co-distillation solvent.

The hydrocarbons used are paraffinic hydrocarbon materials which may be obtained from petroleum distillates which distil at temperatures between 200 and 500 C. This embraces kerosenes distilling above 200 C., low and medium viscosity technical oils and medium and high viscosity medicinal oil fractions which have been treated to remove unsaturated hydrocarbons, waxy materials and at least the main colour-imparting constituents. Such treatment in the production of white oils is well known per se. The resulting white oils have viscosities (Saybolt) of 30-350 seconds: the preferred fractions have viscosities of 50-250 seconds.

It is emphasized that the nature of the liquid paraffin hydrocarbons or mixture thereof and the extent to which it has been refined will depend upon the intended end use of the product. If the product is to be applied to a grow-' ing food crop intended for human or animal consumption, the hydrocarbons must be innocuous and should not harm the plant: they should generally conform to the requirements of purity for liquid paraflins laid down in the British and United States Pharmacopoeias. If the product 3,133,004 Patented May 12, 1964 is intended for use in fiy-killing compositions the degree of refinement required for the hydrocarbons is less stringent, but they should nevertheless be free from objectionable odours and from colouring materials which would stain domestic furniture and furnishing materials. When required for use under conditions other than those noted, e.g. outdoor use on non-food crops, the degree of refinement need not be so high. The preferred materials are those known in the petroleum industry as white oils which are obtained from kerosenes distilling above 200 C., technical and medicinal oil fractions which have first been refined by treatment with sulphuric acid, neutralised and clarifiedsee Dunstan et al., The Science of Petroleum, vol. IV, page 2838 and vol. V, part III, page 189 (Oxford University Press). Examples of suitable materials are (i) the light liquid paraffin of the British Pharmacopoeia which is a mixture of refined liquid parafiins having a kinematic viscosity not greater than 30 centistokes at 37.8" C., (ii) the liquid paraffin of the British Pharmacopoeia which is a mixture of refined liquid paraflins having a kinematic viscosity not greater than 64 centistokes at 37.8" C. and (iii) deodorised and decolorised kerosene fractions distilling above 200 C., preferably freed from aromatic hydrocarbons, such as that sold under the trade name Deobase. Mixtures of such liquid paraffins may also be used as well as other fractions of normally liquid parafiins having comparable boiling points. Mixtures consisting of or comprising fractions having a kinematic viscosity between 20 and 80, preferably between 25 and 70, centistokes at 37.8 C. are very useful.

In carrying out the purification treatment in accordance with the invention the pyrethrum oleoresin extract is first dissolved in the normally liquid parafiin hydrocarbons which are to be used as codistillant and the resulting solution then subjected to distillation at a low pressure. Usually the pressure does not exceed 1 mm. of mercury and is preferably not greater than 0.1 mm. of mercury: most preferably it lies between 10- and 10- mm. of mercury; pressures of 10- to l0 mm. are very suitable. It is preferred to dissolve the oleoresin extract in less than twelve, and preferably'from two to ten, times its volume of liquid paraflin hydrocarbons, but greater or smaller proportions may be used. It should be recognised that the optimum proportions will vary with extracts from different sources, with the structure and relative proportions of the paraffin and cycloparafiin hydrocarbons and with the kind of distillation treatment. The distillation is preferably carried out as a short path distillation and, in its simplest form, results in the pyrethrins being freed from accompanying colouring matters which are objectionable when present in a spraying composition.

According to a feature ofthe invention a partial separation of pyrethrins I and cinerin I from pyrethrin II and cinerin II may be effected during the distillation by separately collecting fractions of different boiling points. It is known that pyrethrin I and cinerin I are more active against certain crawling insects than pyrethrin II. and cinerin II, whilst the latter are more active against certain flying insects. The crude extract may be separated into distillate fractions which are respectively more active against these two kinds of insects than the initial material. Moreover, the production of solutions of the active ingredients in paraffin hydrocarbons in this way enables a user to add additional ingredients,such as synergists, in accordance with his judgment and having due regard, for

I 3 the intended use of the product. When the product is intended for use on crops intended for human consumption considerable care has to be exercised in the selection of such additional ingredients.

A pot still may be used in the process of the invention but a flash still is preferred in order that the time during which the pyrethrum extract is subjected to distillation temperatures is kept to a minimum. The preferred procedure is to maintain the solution of the extract in a storage vessel at a temperature not exceeding 80 C. and then to allow such a degassed preheat solution to flow dropwise into the body of the still where it runs as a film over a surface maintained at a'temperature high enough to enable at-least a part of the volatile materials to distil rapidly across the short path to a condensing tube. The interior of the still is maintained at a low pressure at which the pyrethrins are known to distil without substantial decomposition, e.g. a pressure of l to l0 mm. of mercury or even lower. In this manner the time during which the pyrethrum extract is subjected to the elevated temperature may be reduced to a few minutes or even to a few seconds.

The flash distillation may be carried out in a plurality of stages. To do this the solution of pyrethrum' oleo resin extract is fed to a first short path evaporator in which the temperature of the surface with which the solution is in contact is maintained in the lower part of the range within which mixtures of pyrethrins are volatilised at the low pressure prevailing in the still, e.g. 135- 155 C. at pressures of about l0 mm. of mercury. The

unevaporated portion of the solution from the first evaporator is then led into a second evaporator in which the temperature of the surface with which the evaporating solution is in contact is higher than that in the first evaporator or, alternatively, the pressure is lower, e.g. 160 to 200 C. at pressures at about mm. of mercury. The unevaporated residue from the second still may be fed into a third still in which the temperature of the surface with which the evaporating solution is in contact is higher than that in the second evaporator or, alternatively, the pressure is lower than that prevailing in the second evaporator.

The process of the invention may be used to separate only the more volatile group of pyrethrins predominating in pyrethrin I and cinerin I from the pyrethrum oleo resin extract or to separate the extract into two paraflin hydrocarbon solutions respectively containing (a) pyrethrin I and cinerin I and (b) pyrethrin II and cinerin II as the major active constituents. When carrying out the latter separation more than two separate fractions may be collected, those'of intermediate boiling point being subsequently redistilled. By carrying .out a flash distillation in two or more stages in which the evaporating film is heated in the second or later stage to a higher temperature than that to which it was subjected in the preceding stage a quite substantial degree of separation of the two groups of pyrethrins can be eflected. A relatively large proportion of solvent paraffin hydrocarbons, e.g. 4 to 10' parts per part of extract, also assists in achieving a substantial degree of separation: this is true irrespective of whether distillation in a plurality of stages or pot distillation, separating a plurality of fractions of progressively increasing boiling point, is adopted. By proceeding in this manner a first fraction consisting of pyrethrins and paraflin hydrocanbons and containing 70 to 80% or even more of the total pyrethrins present therein as pyrethrin I and cinerin I and a second, higher boiling fraction consisting of pyrethrins and paraflin hydrocarbons and containing 65 75% or even more of the total pyrethrins present therein as pyrethrin II and cinerin II can be readily obtained.

By using a fraction of liquid paraffin and cycloparaffin hydrocarbons distilling between 250 and 400 C., a codistillation of such hydrocarbons and pyrethrins in which pyrethrin I and cinerin I predominate may be obtained leaving a small residue of hydrocarbons in the undistilled residue which contains the greater part of the pyrethrin II and cinerin II. On the other hand, by using a fraction of liquid paraffin and cycloparafiin hydrocarbons distilling between 250 and 500 C, a first fraction, which is a codistillate, is obtained. This first fraction contains hydrocarbons which predominantly boil between 250 and 380 C., pyrethrin I and cinerin I and is followed by a second higher boiling fraction, which is also a codistillate. The hydrocarbons of the second fraction are predominately those which normally distil between 380 and 450 C. r

The second fraction additionally contains pyrethrins which are mainly pyrethrin II and cinerin II.

The presence of the paraffin hydrocarbons enables the pyrethrins to be distilled at a substantially lower temperature than would otherwise be possible. The inert nature of the hydrocarbons is a valuable property which enables codistillation to occur without providing any opportunity for the reactive centres present in the pyrethrin molecules to enter into reaction other than possibly a small amount of polymerisation. In this way it is possible to distil the pyrethrins at 25 to 50 C. below their boiling points at 10- mm. of mercury absolute pressure in yields of to The isopyrethrin content of the ditsillate is low: that of the first fraction is usually lower than that of the feed material and that of the second fraction is usually about the same as that of the feed material.

When distilled with the paraflin hydrocarbon co-distillant in accordance with the invention, the insecticidal activity of the pyrethrins is retained. The various changes such as polymerisation, inversion, racemisation and isomerisation by movement of the double bonds present in the pyrethrin molecule which are known to be possible are apparently avoided. The distillate is a clear, pale yellow mobile liquid whether collected as a whole or separated into fractions. The distillate or fractions thereof may be diluted with kerosene or other miscible organic liquid to yield solutions which have very little colour and which do not stain.

In the following examples pyrethrum oleo resin extract was subjected to distillation under reduced pressure after mixing with liquid parafiin hydrocarbons distilling between 200 and 500 C. in short path distillation equipment of the pot still type and the flash still type. All parts are by volume for liquids and by weight for vsolids in corresponding units in the c.g.s. system. The isopyrethrin contents of the distillates and residues in the examples are given as the percentage of the total-pyrethrins present which are in the form of isopyrethrins.

Example 1 A mixture of 6.0 parts of pyrethrum oleoresin (35% pyrethrins) and 24 parts of light liquid paraffin is distilled in a pot still and the following fractions separated:

Parts Fraction 1 BR, 75100 C./3 l0 mm; 3.0. Fraction 2 B.P., l00122 C./l0- mm 11.2 Fraction 3 B.P., 122-148" C./5 l0 mm i 7.9

The analyses of thefractions are as follows:

Total (Pyrethrin I Pyrethrins and Oinerin 1)} Percentlso- Distillate Fraction Distilled, (Pyrethrin 1T pyrethrins percent and Cinerin II) Ratio The initial extract used had a (pyrethrin I and cinerin I)/(pyrethrin II and cinerin II) ratio of 1.42 and contained 9.0% of isopyrethrins.

Example 2 g A mixture of 7.5 parts of pyrethrum oleoresin extract (35% pyrethrins), 7.5 parts of liquid parafi'in and 15 parts of light liquid paraffin is distilled in a pot still and the following fractions separated:

Parts Fraction 1 B.P., 70-100 C./9 10- mm 1.5 Fraction 2 B.P., 100-150 C./10 mm 14.2

Fraction 3 BR. 150-175" C./5 10-- mm 4.5

The analyses of the firactious are as follows:

Total (Pyrethrin Pyretln ins I and Oinerin Percent Distillate, Fraction Distilled, I) /(Pyrethrin Isopyrethrins percent II and Cinerin II) Ratio Total 90.1

The initial extract used had a (pyrethrin I and cinerin l)/(pyrethrin II and cinerin H) ratio of 1.42 and contained 9.0% of isop-yrethrins.

Example 3 A mixture of 15 parts of light liquid paraffin, 7.5 parts of liquid parafiin and 8.0 pants of pyrethrum oleoresin extract (25% pyrethrins) is distilled completely in a pot stillwithout separating into fractions at 80-175 C. at a pressure of 10- mm. The distillate is .a clear very pale yellow oil amounting to 20 parts having the following analysis: Total pyrethrins distilled 95.5%; pyrethrin I and cinerin I)/(pyret hrin II and II); ratio 1.34; isopyre-thrin content 11.5%.

The initial pyrethrum extract had a (pyrethrin I and cinerin I/(pyrethrin II and cinerin II) ratio of 1.30 with an isopyrethrin content of 9.6% of the total pyrethrins.

Example 4 A mixture of 16 parts of pyrethrurn oleoresin 25% extract (corresponding to 4.0 parts of pylrethrins I and II and cinerins I and II), 30 parts of light liquid paraffin and parts of liquid parafiin is distilled in a flash distillation plant, the temperature of the hot surface being 158-178" C. and the pressure 1 10 to 3 10 mm. of mercury. There is obtained 48 pants of distillate in the form of a pale yellow oil which contains 3.6 parts of pure pyrethnins I and H and cinenins I and II, that is 91.9% of the initial pyrethrins used. The undistilled residue in the form of a black NlSCld liquid contains 0.21 pants of pyrethrins I and II and cinerins I and II, that is 5.1% of the initial pyrethrins used. The isopyrethrin contents of the initial extract, distillate and residue are: 6.2-6.7%, 4.8-5.1% and 42-54% respectively.

Example 5 A mixture of 8 parts of pyrethrum oleoresin 25% extract (corresponding to 2.0 parts of pyrethiins I and II and cinerins I and H), 24 parts of light liquid parafiin and 8 parts of liquid parafiin is distilled in a flash distillaition plant. The oil before entering the still is maintained at 75 C./ 0.01 mm. of mercury; the temperature of the hot surface is 15 5-1 80 C. and the distillation pres sure 1 10- mm. of mercury. There is obtained 32 parts of distillate as a very pale yellow which contains 1.9,2 parts of pure pyrethrins I and II and cinenins I and E, that is, 96.4% of the initial pyrethrins used. The undistilled residue contained 5.6% of the initial pyrethrins used. The isopyrethn'n contents of the initial extract, distillate and residue are: 6.2-6.8%, 6.5-7.2% and 42.0- 54.0% respectively.

Example 6 A mixture of 16 parts of pyrethrum oleoresin 25% extract (corresponding to 4.0 parts of pure pyrethrins I and II and cinerins I and II), 30 parts of light liquid parafiin and 15 parts of liquid paraflin is distilled in a 5 flash distillation plant, the temperature of the hot surfiace being 160-180 C. and the pressure 1X00" mm. of mercury. There is obtained 43 parts of distillate as a pale yellow oil containing 3.38 parts of pure pyrethrins I and II and cinerins I and II, that is, 84.4% of the initial pyrethm'ns used. The undistilled residue contains 11.4% of the initial pyrethrins used. The isopyrethrin contents of the initial extract, distillate and residue are 5.2-6.0%, 5.8-6.2% and 27.0-32.1% respectively.

Example 7 A mixture of 6 pants of pyrethrum oleoresin 25 extract (corresponding to 0.696 parts of py-rethrin I and cinerin I and 0.670-parts of p-yrethrin I1 and oinerin II), 24 parts of odourless kerosene and 28 parts of light liquid panaflin is distilled in a flash distillation plant consisting or two short path evaporators arranged in series. The walls of each evaporator can be adjusted to different ternperatures; the first being at 100-110 C. and the second at 142-154 C. The internal pressure is 5 10- mm. of mercury.

There are obtained from the first and second evaporators respectively:

(i) 26 parts of distillate as a pale yellow oil containing 0.484 parts of pyrethrin I and cinerin I and 0.205 parts of pyrethr in II and cinerin I I, i.e. 50.4% of the total pyrethrins in the feed. The (pyrethm'n I and cinerin tent of the feed.

I)/(pyrethrin II and cinerin II) ratio is 2.36.

(ii) 20 parts of a pale yellow oil containing 0.198 parts of pyrethrin I and c-inerin I and 0.396 parts of pyrethrin 11 and cinerin II, i.e. 43.5% or" the total pyrethrins in the feed. The (pyrethrin I and cinerin I) /(pyrethrin H and cinerin II) ratio is 0.50.

The isopyrethrins contento f the feed, first traction distillate and second fraction distillate are: 9.5%, 8.0% and 10.0% respectively-of the total pyrethrins present in each fraction.

The yield of total distilled pyrethrins is 93.8% of the feed; the residue contains 6.2% of the pyrethrins in the feed.

Example 8 A mixture or 8 part of pyrethrum oleoresin 25% extract (corresponding to 0.886 parts of pyrethrin I and cinenin I and 0.854 parts of pyrethrin II and cinerin II) and 48 parts of light liquid paraffin is distilled in the plant described in Example 7.

The temperatures maintained in the first and second evaporators are 104-116 C. and ISO-166 C. respectively; the pressure is 1X10" mm. of mercury.

There are obtained from the first andsecond evaporators:

(i) 26 parts of a pale yellow oil containing 0.648 parts of pyrethrin I and oinerin I and 0.358 pants of pyrethrin II and cinerin II, i.e. 57.8% of the total pyrethn'ns con- (Isopyrethn'n content of feedand distillate are 9.0% and 7.0% respectively of total pyrethrins presents.) The (pyrethrin I and cinerin I) (pyrethrin II and cinerin II) content is 1.81.

(ii) 18-parts of pale distillate containing 0.214 parts of pyrethrin I and ciner-in I and 0.416 parts of pyrethrin II and ciner-in II, i.e. 36.2% of the total pyrethrins content of the feed. (Isopyrethrins content 8.5% of total pyrethrins.) The (pyrethrin l and .c-inerin I)/ (pyrethrin II cinerin II) ratio is 0.52.

The total recovery of distilled .pyrethrins is 94%.

Example 9 A mixture of 10 parts of py-rethrin oleoresin 25% extract (corresponding to 1.150 parts of 'pyrethrin I and cinerin I and 1.105 parts of pyrethrin II and ciner-in II) and 28 parts of a light liquid paraifin is distilled in the plant described in Example 7. The temperatures of the first andsecond ewaporators are -115 C. and C. respectively. The internal pressure is 1X10- mm. of mercury.

There are obtained from the first and second evaporators:

(i) 20.9 parts of a pale yellow oil containing 0.952 parts of pyrethrin I and cinerin I and 0.583 parts of pyrethrin l1 and cinerin II, i.e. 68.1% of the feed pyrethnins. I The (pyrethrin I and cinerin I)/(pyrethrin II and cinerin II) ratio is 1.60.

(ii) 9.16 parts of a pale oil containing 0.158 pants of pyrethrin I and cinerin I and 0.383 parts pyrethrin II and cinerin I-I, i.e. 24.0% of the initial feed. The (pyreand cinenin I)/(pyrethrin II and cinerin I I) ratio The isopyrethrins content of the feed, first fraction distillate, second fraction distillate and undistilled residue is 9.2%, 7.2%, 14.0% and 45% respectively calculated as the percentage of total pyrethrins present in the fractron.

We claim:

1. A process for purifying a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof which process comprises distilling, under reduced pressure, a solution of about one part by volume pyrethrum oleoresin extract and two to twelve parts by volume of a fraction of liquid paraifinic hydrocarbons of boiling range 200 to 500 C., and condensing the resultant distillate, thereby obtaining a composition of liquid hydrocarbon, pyrethrin andcinerin.

2. A process for purifying 1a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof, which process comprises distilling, under an absolute pressure of at most one millimeter of mercury, a solution of about one part by volume of pyrethrum oleoresin extnact and two to twelve parts by volume of a fraction of liquid parafiinic hydrocarbons of boiling range 200 to 500 C., and condensing the resultant distillate, thereby obtaining composition of liquid hydrocarbon, pyrethrin and cinerin.

3. A process for purifying a pyrethrin-containing com position without impairing the insecticidal activity of active components thereof, which process comprises (1) distilling, under an absolute pressure of at most one millimeter of mercury, a solution of about one pant by volume of pyrethrin oleoresin extract and two to twelve parts by volume of a fraction of liquid panaffinic hydrocan'bons of boiling range 200 to 500 C.,

(2) separately condensing, as one fraction, a vaporous admixture comprising the more volatile of said hydrocarbons and the more volatile pyrethrins rich in pyrethrin I and cinerin I and, as a second traction distillingat a higher temperature, an admixture comprising the less volatile of said hydrocarbons and the less volatile pyrethrins rich in pyrethrin II and cinerin II.

4. A process for purifying a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof, which process comprises (1) distilling, under an absolute pressure of at most one millimeter of mercury, a solution of about one part by volume of pyrethrum oleoresin extnact and two to twelve par-ts by volume of liquid *white oil boiling range 250 to 500 C., and

(2) separately condensing, as one fraction, a vaporous admixture comprising the more volatile hydrocarbons present in said white oil and the more volatile pyrethrins rich in pyrethrin I and cinerin I and, as a second fraction distilling at a higher temperature, an admixture comprising the less volatile hydrocarbons present in said white oil and the less volatile pyrethrins rich in pyrethrin II and cinerin II.

5. A process for purifying a pyrethiin-containing composition without impairing the inseoticidal activity of active components thereof, which process comprises (1) distilling, at a pressure within the range of from 0.1 millimeter to 1 10 millimeter of mercury,

a solution of about one part by volume of pyrethrum oleoresin extract and two to twelve parts by volume of liquid white Oil of boiling range 250 to 500 C., and

(2) separately condensing, as, one fraction, a vaporous admixture comprising the more volatile hydrocarbons present in said white oil and the more volatile pyrethrins rich .in pyrethrin I and cinerin -I and, as a second fraction distilling-art a higher temperature, an admixture comprising the less volatile hydrocarbons present in said White oil and the less volatile pyrcthrins rich in pyrethrin II and cinerin II.

v 6. A process for purifying a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof, which process comprises (1) passing solution of about one part by volume of pyrethrum oleoresin extract and two to twelve parts by volume of a fraction of liquid paraffinic hydrocarbons of boiling range 200 to 500 C. through a plurality of low pressure evaporators,

(2) distilling said solution at an absolute pressure of at most one millimeter of mercury at a first temperature, at which temperature the more volatile of said hydrocarbons and the more volatile of the pyrethrins are vaporized,

(3) condensing the resultant vapor from (2),

(4) distilling the unvaporized residue at a second temperature higher than said first temperature, at which second temperature the less volatile of said hydrocarbons and the less volatile of the pyrethrins are vaporized, and

(5) condensing the resultant vapor from (4).

7. A process for purifying a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof, which process comprises (1) passing solution of about one part by volume of pyrethrum oleoresin extract and two to twelve parts by volume of liquid White oil of boiling range 250 to 500 vC. through a plurality of low pressure evaporators,

(2) distilling said solution at an absolute pressure of at most one millimeter of mercury at a first temperature, at which temperature the more volatile of said hydrocarbons and the more volatile of the pyrethrins are vaporized,

(3) condensing the resultant vapor from (2),

' (4) distilling the unvaporized residue at a second temperature higher than said first temperature, at which second temperature the less volatile of said hydrocarbons and the less volatile of the pyrethrins are vaporized, and

(5) condensing the resultant vapor from (4).

8. A process for purifying a pyrethrin-containing composition without impairing the insecticidal activity of active components thereof, which process comprises (1) passing solution of about one part by volume of pyrethrum oleoresin extract and two to twelve parts by volume of liquid white oil of boiling range 250 to 500 C. through a plurality of low pressure evaporators, I

(2) distilling said solution at an absolute pressure within the range of from 0.01 millimeter to 1X 10- millimeter of mercury at a first temperature, at which temperature the more volatile of said hydrocarbons and the more volatile of the pyrethrins are vaporized,

(3) condensing the resultant vapor from (2),

(4) distilling the unvaporized residue at an absolute pressure within the range of from 0.01 millimeter to 1 10 millimeter of mercury and at a second temperature higher than said first temperature, at which second temperature the less volatile of said hydrocarbons and the less volatile of the pyrethrins are vaporized, and

(5) condensing the resultant vapor from (4).

9. A process for purifying a pyrethrin-ccntaining com- 9 10 position without impairing the insecticidal activity of accomposition by distillation, the improvement comprising tive components thereof, which process comprises distilling, at an absolute pressure of at most one milli- (1) passing solution of about one part by volume of meter of mercury, a solution of one part by volume of pyrethrum oleoresin extract and four to ten parts pyrethrum oleoresin extract and two to twelve parts by by volume of liquid white oil of boiling range 250 5 volume of a fraction of liquid paraflinic hydrocarbons of to 500 C. through a plurality of low pressure evapboiling range 200 to 500 0, thereby forming a distillate orators, composition rich in pyrethrins without impairing the in- (2) distilling said solution at an absolute pressure withsecticidal properties of same.

in the ran e of from 0.01 millimeter to 1 10- millimeter (if mercury at a first temperature, at which 10 References Clted m the file of this patent temperature the more volatile of said hydrocarbons UNITED STATES PATENTS and the more volatile of the pyrethrins are vaporized, 1 940 54 m 19 1933 o de the resultapt p r from 2,358,392 Goodhue et a1 Sept. 19, 1944 a g llllnvaporlzeg g a 2,423,545 Aeschbach July 8, 1947 pressure w1 nt erange o om m1 rme er 0 15 1 10- millimeter of mercury and at a second tem- FOREIGN PATENTS perature higher than said first temperature, at which 656,058 Great Britain Aug. 8, 1951 second temperature the less volatile of said hydrocarbons and the less volatile of the pyrethrins are T T IFEFERENCES vanorized, and 20 Welssberger: Distillation, volume IV, Interscrence 5 ondensing h resultant vapor f 4 Publishers, Inc., New York, 1951, pages 3174520 and 10. In a process for purifying a pyrethrin-containing 356485- 

1. A PROCESS FOR PURIFYING A PYRETHRIN-CONTAINING COMPOSITION WITHOUT IMPAIRING THE INSECTICIDAL ACTIVITY OF ACTIVE COMPONENTS THEREOF WHICH PROCESS COMPRISES DISTILLING, UNDER REDUCED PRESSURE, A SOLUTION OF ABOUT ONE PART BY VOLUME PYRETHRUM OLEORESIN EXTRACT AND TWO TO TWELVE PARTS BY VOLUME OF A FRACTION OF LIQUID PARAFFINIC HYDROCARBONS OF BOILING RANGE 200* TO 500*C., AND CONDENSING THE RESULTANT DISTILLATE, THEREBY OBTAINING A COMPOSITION OF LIQUID HYDROCARBON, PYRETHRIN AND CINERIN. 